Base for color copying screens



March 2s, 1939..

" F. PILLER u 2,152,621

` A BASE FOR COLOR COPYING SCREENS Filed May 29, 1936 PRPEH AA/5N ron ,arras/wey.

Patented Mar. 28, 1939 UNITED STATES PATENT OFFICE sppnciz sassi Juno 4. 1935 The bases employed for color copying screens consist mainly 'of a paper foil faced with a thin layer of metal serving to increase the brilliancy of the colored copy and to allow of the expansion of the paper without detriment to the film of metal. It is also part of the prior art to provide the metal lm with one or more waterproof or reective coats in order to eliminate detrimental chemical or other action between the metal, the

all such cases it has been the rule to choose the metal layer of exceeding thinness and to make the paper base several times as thick as the metal layer, the paper base thus forming a substantially independent body.

In practice it has been found that a base of the above described kind does not possess the absolutely necessary insensibility to exterior iniiuences (temperature, humidity, etc.) required to ensure the permanency of the screen lines, because the thin metal iilm is not strong enough to resist the stresses acting on the much thicker paper base and therefore expands or contracts in the same measure as the latter.

Thepresent invention refers to a base for color copying screens which is entirely independent of the elastic changes of form on the part of the other units of the screen, remaining entirely. un-

changed both before and especially during the printing or ruling of the screen, so that the screen lines cannot become distorted, thus ensuring perfect registration with the screened negative.

By way of an example, the invention is illustrated by the drawing in which the gure comprises afbriefed vertical section through the device. f

According to the present invention the screen base consists essentially of a metal foil l of a sufficiently hard material with a coeiiicient of expansion so small that it can be practically neglected, as is, for instance, the case with aluminium and combinations of aluminium with another material or materials. This metal foil acts as a carrier or base' for all further layers 2, 3, 4, 5, 6 and 1 which may be arranged in the usual manner and number on the face or back of the foil.

The layers destined for the upper side or face of the foil may comprise, for instance, two different groups arranged between the metal foil and thecolor screen system. One group serves as a coat for the metal and the second as a reecting background. The provision of` reiiective protecting coatings (for instance,l of white lacquer) on metal for photographic purposes is in 55 itself a'part Yof the prior art, but such cases screen colors and the'photographic emulsion. In

quer or similar material, which will neutralize the 10n dark tone of the first coating. If, however, the rst coating 6 is of a sufciently light shade of color, the second layer may be dispensed with as shown in the drawing. In any case themetallic reaction will be entirely eliminated.

The second group of layers is now arranged on the top of the rst group, the iirst layer of this second group serving as reflective layer 2 and consists, for instance, of baryta gelatine; onV this is arranged a layer of transparent lacquer I 20 to prevent penetration of the ink or other medium used for ruling the color screen into the reective layer. On this fourth (or third) layer the color screen system 3, consisting. of lines or the like, is now printed and then this screen sysotem coated with emulsion 4.

The arrangement that each layer or each group of layers serves for a certain purpose makes it possibleto permanently eliminate the detrimental reaction of metal, coloring matter and emulsion on each other and thereby to ensure perfect and eiiicient operation of the screen. Itis immaterial for the purposes of this invention how many single layers are employed for each group of layers; under certain conditions it may be possible to employ a single layer in place of each group, or even in place of both groups.

A further layer, for instance, of thin paper 5 or other suitable material, may be arranged on the back of the metal foil, in order to,hide the bright metallic surface and to prevent the metallic noise ensuing when piling or handling the naked foils. But in all -cases the resistance to distortion of the metal foil will be greater than the sum of all stresses of the individual layers, so that these stresses will not be able to cause distortion (expansion or contraction) of the metall foil. Since these layers are very thin, a thickness ofthe metal foil of a few hundredths of a millimetre, for instance, of about 900ths mm., will as a rule be found suiiicient.

What I claim as my invention, is:

1. A foundation for a color copying screen comprising a sheet of metal foil, the metal of said foil having a low expansion coeiiicient, a moisture rev pellent layer on one surface of said foil, a reneetive layer superimposed upon said first layer, said foil having a strength greater than -the total' having low expansion Ycoecient, a'inoisture repellent layeron one surface of said foil,y and a reiective layer superimposed upon said rst layer,

said foil having a strength greater than the total strength of said layers to prevent the expansion and contraction thereof. 

